1. Field of the Invention
The present invention relates to the substrate for an ink jet recording head. The invention also relates to an ink jet recording head, and a method of manufacture therefor.
2. Related Background Art
The ink jet recording method disclosed in the specifications of U.S. Pat. No. 4,723,129, U.S. Pat. No. 4,740,796, or the like makes it possible not only to record at high-speed and in high-density, as well as in high image quality, but also, to facilitate forming images in colors with a more compact apparatus. This method has, therefore, attracted more attention of those in the art in recent years particularly.
For the recording head of ink jet recording type, which is arranged to enable ink to bubble by the utilization of thermal energy for discharging ink to a recording medium, it is generally practiced to arrange the structure so that the heat generating resistive members that enable ink to bubble, and the wiring that makes electric connections are incorporated on the same substrate, hence providing an ink jet recording head substrate. Also, the nozzles for discharging ink are formed on the substrate thus provided.
The ink jet recording head substrate is then devised in various ways from the viewpoint of providing a smaller structure and more convenience on one hand, and form the viewpoint of saving the input of the electrical energy on the other hand. There are many devices provided, in particular, for the configuration of the heat generating resistive member connected with the wiring, which forms the heat generating unit, as well as for the arrangement thereof. Then, as the most popular structure, the heat generative resistive material is arranged on the lower layer, and the electrode layer, which is formed by Al material, is arranged on the upper layer in order to form a two-layer structure, and then, the Al on the heat generating portions is removed. In this way, the resistance of each of the heat generating portions becomes higher, and when current flows, thermal energy is generated to enable ink to bubble. Also, on each of the heat generating portions, the protection film is formed to protect the heat generating resistive member and wiring. Thus, the structure of this protection film is one of the important factors, such as the power dissipation and the life thereof, to determine the performance of an ink jet head.
However, with the conventional structure of the protection film, the requirement of the lower power dissipation is eventually incompatible with the enhancement of the film reliability which is need for the maintenance of the longer life of a head.
For example, the lower the power dissipation for ink bubbling, the thinner is the thickness of the film required when provided for the surface that contacts with ink and the heat generating resistive member, and also, the heat transfer ratio thereof should be larger, because, in such arrangement, the escape of heat to the sides other than ink side should be made smaller. In other words, the thinner the protection film, the better the energy efficiency. On the other hand, however, if the protection film is thinner, pin holes may take place on the protection film or it becomes impossible to cover the stepping portions of wringing sufficiently. As a result, ink may enter such portions to erode wiring or to cause the erosion of the heat generating resistive members, thus affecting the reliability of the head, and also, making the life thereof shorter.
In this respect, it is known that the film quality of the protection film is enhanced by making the temperature higher at the time of film formation. However, if the temperature becomes 400xc2x0 C. or more at the time of forming a protection film, for example, the development of hillocks or the like becomes apparently noticeable in the protection film due to the presence of the Al wiring. Consequently, even if the film quality becomes better on the stepping portions, the Al wiring is subjected to erosion due to the development of the hillocks after all. In order to prevent the erosion of wiring due to the hillocks of the kind, it is necessary to arrange the protection film to be thick enough at least on the wiring portions.
Here, it is possible to evade this question of the hillock development on the Al wiring if the arrangement order of the Al wiring and the heat generating resistive member is inverted. However, with the structure that may be arranged in such order, the film quality of the heat generating resistive member becomes inferior on the stepping portions, because the heat generating resistive member should be in contact with the stepping portions of the Al wiring. As a result, the resistive value of each member becomes greatly varied, and problems are encountered when the members are used actually.
To deal with a problem of the kind, there is disclosed a structure in the specification of Japanese Patent Application Laid-Open No. 08-112902 which makes it possible to lower the power dissipation by making the portions of the protection film thinner on the portions related to bubbling, and at the same time, to enhance the film reliability for the longer life thereof.
In other words, the disclosed structure is formed in the processing steps of preparing a substrate provided with a plurality of heat generating resistive members to give heat to ink, a plurality of wiring connected with each of the heat generating resistive members, and a plurality of heat generating portions formed on the aforesaid heat generating resistive members, which are exposed from the wiring; in the step of covering the heat generating resistive member and wiring on the substrate with a first insulating protection film; of removing the portions of the first insulating protection film on the heat generating portions by means of the wet etching; and in the step of covering the first insulating protection film with a second insulating protection film. In this manner, the etched portions of the first insulating protection film of the heat generating portions in the longitudinal direction are arranged on the inner side by xc2xd or more of the sum of the thickness of the first and second insulating protection films that cover each area from the end of the heat generating portion to the wiring.
In this respect, each of the heat generating resistive members generates heat all over the surface. However, such heat is allowed to escape from the circumference of each of them greatly. As a result, the temperature becomes lower on circumferential portions, and does not contribute to bubbling eventually. This bubbling condition is observed carefully. As a result, it is ascertained that bubbling is effectuated only on the area which is approximately 4 xcexcm inside (this area is referred to as the effective bubbling area) in the direction from the circumference of each heat generating resistive member toward the inner side thereof. In accordance with the structure disclosed in the above-mentioned specification of the laid-open application, the thicker portion of the protection film covers even the fundamentally effective bubbling area of each heat generating resistive member. Because of this coverage, the actually effective bubbling area becomes smaller in some cases. The reduction of the effective bubbling area is not regarded as a very serious problem as far as the arrangement pitches of nozzles are not very high. However, if nozzles should be arranged in higher density, the area of the heat generating resistive members becomes smaller with the thickness of the electrodes remaining almost unchanged. Therefore, this problem becomes no longer negligible.
Now, with a view to solving the problems discussed above, the present invention is designed. It is an object of the invention to provide the substrate for an ink Jet recording head capable of making the life thereof longer in order to enhance the reliability even with the adoption of the thinner film.
Also, it is another object of the invention to provide the substrate for an ink jet recording head having measures as to the effective temperature reduction on the circumference of each of the heat generating resistive members, as well as the maintenance of the longer life thereof to enhance the reliability even with the adoption of the thinner film as described above.
In order to achieve the above-mentioned objectives, the present invention is characteristically structured as given below.
In other word, the ink jet recording head substrate of the present invention is provided with a plurality of heat generating resistive members and the electrode wiring pattern electrically connected with the heat generating resistive members formed on the substrate, and a protection film formed on the heat generating resistive members and the electrode wiring pattern to protect them from ink. For this substrate, each of the heat generating resistive members comprises a first heat generating resistive member arranged on the lower layer of the electrode arrangement pattern connected with the heat generating resistive member, and a second heat generating resistive member arranged between the protection film and the electrode arrangement pattern.
Also, the ink jet recording head of the present invention is provided with an ink jet recording head substrate having a plurality of heat generating resistive members and the electrode wiring (arrangement) pattern electrically connected with the heat generating resistive members formed on the substrate, and a protection film formed on the heat generating resistive members and the electrode wiring pattern to protect them from ink; discharge ports for discharging ink; and liquid paths communicated with the discharge ports. For this ink jet recording head, each of the heat generating resistive members comprises a first heat generating resistive member arranged on the lower layer of the electrode wiring pattern connected with the heat generating resistive member, and a second heat generating resistive member arranged between the protection film and the electrode wiring pattern.
Also, the method of the present invention for manufacturing an ink jet recording head provided with an ink jet recording head substrate having a plurality of heat generating resistive members and the electrode wiring pattern electrically connected with the heat generating resistive members formed on the substrate, and a protection film formed on the heat generating resistive members and the electrode wiring pattern to protect them from ink; the discharge ports for discharging ink; and the liquid paths communicated with the discharge ports, comprising the steps of forming first heat generating resistive members on the substrate; forming the electrode wiring pattern connected with the first heat generating resistive members on the first heat generating resistive members with the exception of the heat generating portions of the heat generating resistive members; covering the electrode wiring pattern with second heat generating resistive members; and forming the protection film on the second heat generating resistive members.
In accordance with the present invention, the structure is formed so that the upper and lower heat generating members are arranged with the electrodes connected with the heat generating resistive members sandwiched between them. Thus, it is made possible to make the protection film on the upper layer thinner to attempt the power saving. Also, there is no need for making the effective bubbling area smaller, hence providing a highly reliable ink jet recording head operational in high density.